Aged cheddar

A hard cow milk cheese aged for 9 months or longer. Ageing breaks the protein down, which gives the sharp, savoury taste. The same breakdown makes it melt badly on its own. The proteins form small tight groups that hold on to each other when heated, and the fat leaks out as grease. Mix it with a younger, more elastic cheese, or use sodium citrate. Grate it fine so it melts evenly.